SATA RAID Contollers - The Weakest Link...

Joined
Dec 5, 2003
Messages
517
You have a 16-port SATA RAID controller and 16 SATA300 drives in RAID0 (this is only an example to understand a concept). What is going to be the max theoritical speed of the array (MBps), or in other words what is going to be the limiting factor: the SATA300 standard, the controller, the bus the controller is on (PCI, PCI-E)...

I guess what I am trying to establish is if there is a limit to the number of drives a controller card can support? I saw 8-port controllers advertised as 2 channel... I was under the impression each SATA connection is a separate channel.

Can anyone clarify this?
 

pissboy

Gawd
Joined
Feb 2, 2003
Messages
514
The limit is usually the controller. The Areca IOP341 controllers max out at around 600-800MB/s with 8-12 drives, any more drives and the controller is still the limiting factor.
 
Joined
Dec 5, 2003
Messages
517
The manufacturer fails to mention why these controllers have two channels and their peak bandwidth. Furthermore, what is the maximum number of devices you can have per channel...
 

mindedc

n00b
Joined
Jul 7, 2008
Messages
22
In my not so humbe experience, the limiting factor is whatever you are copying data to/from or the software in the system or the network. I have done a lot of network and application benchmarks and usualy it's either a mis-config, or a limitation in some piece of software or hardware.

If you are just copying to and from single drives either local or across the network, then you will need lots of other drives to start eating into the performance of such an array. If its across a network, it needs to be gigabit. You would want to make certain you use a good network card like an Intel server card, not a piece of crap like a realtek. The crappy cards of course don't loose traffic, they just increase system load. You will also want to use jumbo frame as well as a switch with lots of buffer space, so you are talking about a fairly expensive switch, especially if you buy from a company like Cisco that charges a super premium for performance. You will then need to make certain your protocol doesn't have any issues, I.E. reduced block size by SMB signing or use something more efficient..... If you want real performance, dump windows networking and use something leaner for the transfer like robocopy or cpio+netcat. At that point you would also be optimizing your TCP stack and disabling nagle's algorithm.....Its endless.

If this is for your house, basically don't worry about it, get a modern card, modern drives, battery backup to enable write caching (writes are the worst performance problem on RAID) and enjoy your hardware. If this is for your business, get a good consultant in there who has done this before. It will cost you, but its worth it for the performance if you need it. If you don't need that much performance, go back to not worrying about it.

One more thing, if you are running a database server on this, you need a totally different disk config from a file server. Definitely get an expert on that database to do the disk layout.
 

Blue Fox

[H]F Junkie
Joined
Jun 9, 2004
Messages
11,814
Definitely controller. Having used different size arrays on multiple controllers, you can see where their limit is. My Areca 1280ML (IOP341) won't go higher than ~750mb/s (storport drivers) no matter how many drives. My Areca 1130ML (IOP331) wouldn't go higher than ~400mb/s. I believe the IOP348 tops out at around 1gb/s, but I don't have a drive controller that has one, so I can't validate that. The 1280ML is PCI-e 8x while the 1130ML is PCI-X (133mhz), so the bus speed is not the limiting factor. Do you need more than 750mb/s (or possibly 1gb/s)? If so there are some options, but we'll get back to that.

As for the number of drives a controller can support, my 1280ML is 24 port (6 SFF8087 connectors), so 24 drives. If you get a SAS controller however, you can run quite a lot more SATA drives (or SAS) if you use expanders. The Areca cards are limited to 128 drives as far as I know, but SAS spec allows for up to 16384 devices (drives, controllers, expanders, etc). Also, some SATA drive controllers support port multipliers, but they are limited and I can't think of any decent hardware RAID controllers that do, so I wouldn't worry about them too much.
 
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